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C07C401/00—Irradiation products of cholesterol or its derivatives; Vitamin D derivatives, 9,10-seco cyclopenta[a]phenanthrene or analogues obtained by chemical preparation without irradiation

C—CHEMISTRY; METALLURGY

C07—ORGANIC CHEMISTRY

C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS

C07C35/00—Compounds having at least one hydroxy or O-metal group bound to a carbon atom of a ring other than a six-membered aromatic ring

C07C35/22—Compounds having at least one hydroxy or O-metal group bound to a carbon atom of a ring other than a six-membered aromatic ring polycyclic, at least one hydroxy group bound to a condensed ring system

C07C35/23—Compounds having at least one hydroxy or O-metal group bound to a carbon atom of a ring other than a six-membered aromatic ring polycyclic, at least one hydroxy group bound to a condensed ring system with hydroxy on a condensed ring system having two rings

C07C35/32—Compounds having at least one hydroxy or O-metal group bound to a carbon atom of a ring other than a six-membered aromatic ring polycyclic, at least one hydroxy group bound to a condensed ring system with hydroxy on a condensed ring system having two rings the condensed ring system being a (4.3.0) system, e.g. indenols

Abstract

Disclosed are methods of purifying the compound (20R,22R)-2-methylene-19-nor-22-methyl-1α,25-dihydroxyvitamin D3 to obtain the compound in crystalline form. The methods typically include the steps of dissolving a product containing the compound in a solvent comprising hexane and 2-propanol, cooling the solvent and dissolved product below ambient temperature for a sufficient amount of time to form a precipitate of crystals, and recovering the crystals. Certain diol precursors formed during the synthesis of the compound and its diasteromers also may be obtained in crystalline form using ethyl acetate as a solvent.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application claims the benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/652,954, filed on May 30, 2012, the content of which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under DK047814 awarded by the National Institutes of Health. The government has certain rights in the invention.

BACKGROUND

The field of the present invention relates to purification of organic compounds, and more particularly to the purification of the compounds (20R,22R)-2-methylene-19-nor-22-methyl-1α,25-dihydroxyvitamin D3 (referred to herein as “SAG-2”) as well as certain diol precursors (referred to herein as “Diol-1,” “Diol-2,” and “Diol-3”), formed during the synthesis of the (20R,22S), (20R,22R), (20S,22R) and (20S,22S) diastereomers of 2-Methylene-19-nor-22-methyl-1α,25-dihydroxyvitamin D3 (referred to herein as “SAG-1,” “SAG-2,” “AGS-1” and “AGS-2” respectively), by preparing the compounds in crystalline form.

Purification of organic compounds, especially those designated for pharmaceutical use, is of considerable importance for chemists synthesizing such compounds. Preparation of the compound usually requires many synthetic steps and, therefore, the final product can be contaminated not only with side-products derived from the last synthetic step of the procedure but also with compounds that were formed in previous steps. Even chromatographic purification, which is a very efficient but relatively time-consuming process, does not usually provide compounds which are sufficiently pure to be used as drugs.

Depending on the method used to synthesize 1α-hydroxyvitamin D compounds, different minor undesirable compounds can accompany the final product. Thus, for example, if direct C-1 hydroxylation of the 5,6-trans geometric isomer of vitamin D is performed, followed by SeO2/NMO oxidation and photochemical irradiation, (see Andrews et al., J. Org. Chem. 51, 1635 (1986); Calverley et al., Tetrahedron 43, 4609 (1987); Choudry et al., J. Org. Chem. 58, 1496 (1993)), the final 1-hydroxyvitamin D product can be contaminated with 1β-hydroxy- as well as 5,6-trans isomers. If the method consists of C-1 allylic oxidation of the 4-phenyl-1,2,4-triazoline-3,5-dione adduct of the pre-vitamin D compound, followed by cycloreversion of the modified adduct under basic conditions, (see Nevinckx et al., Tetrahedron 47, 9419 (1991); Vanmaele et al., Tetrahedron 41, 141 (1985) and 40, 1179 (1994); Vanmaele et al., Tetrahedron Lett. 23, 995 (1982)), one can expect that the desired 1α-hydroxyvitamin can be contaminated with the pre-vitamin 5(10), 6,8-triene and 1β-hydroxy isomer. One of the most useful C-1 hydroxylation methods, of very broad scope and numerous applications, is the experimentally simple procedure elaborated by Paaren et al., J. Org. Chem. 45, 3253 (1980); and Proc. Natl. Acad. Sci U.S.A. 75, 2080 (1978). This method consists of allylic oxidation of 3,5-cyclovitamin D derivatives, readily obtained from the buffered solvolysis of vitamin D tosylates, with SeO2/t-BuOOH and subsequent acid-catalyzed cycloreversion to the desired 1α-hydroxy compounds. Taking into account this synthetic path it is reasonable to assume that the final product can be contaminated with the 1α-hydroxy epimer, the 5,6-trans isomer and the pre-vitamin D form. 1α-hydroxyvitamin D4 is another undesirable contaminant found in 1α-hydroxyvitamin D compounds synthesized from vitamin D2 or from ergosterol. 1α-hydroxyvitamin D4 results from C-1 oxidation of vitamin D4, which in turn is derived from contamination of the commercial ergosterol material. Typically, the final product may contain up to about 1.5% by weight 1α-hydroxyvitamin D4. Thus, a purification technique that would eliminate or substantially reduce the amount of 1α-hydroxyvitamin D4 in the final product to less than about 0.1-0.2% would be highly desirable.

The vitamin D conjugated triene system is not only heat- and light-sensitive but it is also prone to oxidation, leading to the complex mixture of very polar compounds. Oxidation usually happens when a vitamin D compound has been stored for a prolonged time. Other types of processes that can lead to a partial decomposition of vitamin D compounds consist of some water-elimination reactions. The driving force for these reactions is the allylic (1α-) and homoallylic (3β-) position of the hydroxy groups. The presence of such above-mentioned oxidation and elimination products can be easily detected by thin-layer chromatography.

Usually, all 1α-hydroxylation procedures require at least one chromatographic purification. However, even chromatographically purified 1α-hydroxyvitamin D compounds, although showing consistent spectroscopic data that suggests homogeneity, do not meet the purity criteria required for therapeutic agents that can be orally, parenterally or transdermally administered. Therefore, it is evident that a suitable method of purification of 1α-hydroxylated vitamin D compounds such as SAG-2 is required.

SUMMARY

Disclosed herein are methods of purifying the compound SAG-2 as well as certain diol precursors of the compound (Diol-1, Diol-2, or Diol-3), which are formed during the synthesis of SAG- and SAG-2. The purification methods typically include a crystallization step to obtain SAG-2 as well as the desired diol precursors Diol-1 and Diol-2 in crystalline form. The solvent plays an important role in the crystallization process, and is typically an individual liquid substance or a suitable mixture of different liquids. For crystallizing SAG-2, as well as the desired diol precursors Diol-1, Diol-2, or Diol-3, the most appropriate solvent and/or solvent system is characterized by the following factors:

Interestingly, hexane, so frequently used for crystallization purposes, was found less suitable as the sole solvent for crystallization of SAG-2 or any of the diol precursors Diol-1, Diol-2 or Diol-3. However, it was found that ethyl acetate was most useful as the sole solvent for the crystallization of the diol precursors Diol-1, Diol-2 and Diol-3, and a mixture of 2-propanol and hexane, was most useful for the crystallization of the end product SAG-2. In particular, it was determined that a mixture of about 10% to about 20% 2-propanol (v/v) with about 90% to about 80% hexane (v/v) (and preferably 15% 2-propanol (v/v) with about 85% hexane (v/v)) performed well. The ethyl acetate solvent and the 2-propanol/hexane solvent mixture were easy to remove by evaporation or other well-known methods. In all cases the crystallization process occurred easily and efficiently. The precipitated crystals were sufficiently large to assure their recovery by filtration or other means, and thus were suitable for x-ray analysis.

Accordingly, disclosed is a compound having the formula:

in crystalline form. More specifically, the compound may be referred to as (20R,22R)-2-methylene-19-nor-22-methyl-1α,25-dihydroxyvitamin D3 or “SAG-2”, which has the above illustrated structural formula, in crystalline form.

Also disclosed is a compound having the formula

in crystalline form, where the wavy line at carbon 22 indicates the methyl group attached to carbon 22 may be in its R or S orientation. More specifically, disclosed are (8S,20R,22S)-Des-A,B-22-methyl-cholestan-8,25-diol (Diol-1) in crystalline form, and (8S,20R,22R)-Des-A,B-22-methyl-cholestan-8,25-diol (Diol-2) in crystalline form.

Further, disclosed is a compound having the formula

in crystalline form. More specifically, the compound may be referred to as (8S,20S,22R)-Des-A,B-22-methyl-cholestan-8,25-diol (Diol-3) in crystalline form.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the three dimensional molecular structure for SAG-2 as defined by the atomic positional parameters discovered and set forth herein.

FIG. 2 is an illustration of the three dimensional molecular structure for Diol-1 as defined by the atomic positional parameters discovered and set forth herein.

FIG. 3 is an illustration of the three dimensional molecular structure for Diol-2 as defined by the atomic positional parameters discovered and set forth herein.

FIG. 4 is an illustration of the three dimensional molecular structure for Diol-3 as defined by the atomic positional parameters discovered and set forth herein.

DETAILED DESCRIPTION

Disclosed herein is the compound (20R,22S)-2-methylene-19-nor-22-methyl-1α,25-dihydroxyvitamin D3 (SAG-1), characterized by the formula I shown below:

Also disclosed herein is the compound (20R,22R)-2-methylene-19-nor-22-methyl-1α,25-dihydroxyvitamin D3 (SAG-2) in crystalline form, a pharmacologically important compound, characterized by the formula II shown below:

Also disclosed herein is the compound (8S,20R,22S)-Des-A,B-22-methyl-cholestan-8,25-diol (Diol-1) in crystalline form. Diol-1 is the precursor of SAG-1 formed during the synthesis of SAG-1, and is characterized by the formula III shown below:

Also disclosed herein is the compound (8S,2R,22R)-Des-A,B-22-methyl-cholestan-8,25-diol (Diol-2) in crystalline form. Diol-2 is the precursor of SAG-2 formed during the synthesis of SAG-2, and is characterized by the formula IV shown below:

Also disclosed herein is the compound (20S,22R)-2-methylene-19-nor-22-methyl-1α,25-dihydroxyvitamin D3 (AGS-1), characterized by the formula V shown below:

Also disclosed herein is the compound (20S,22S)-2-methylene-19-nor-22-methyl-1α,25-dihydroxyvitamin D3 (AGS-2), characterized by the formula VI shown below:

Also disclosed herein is the compound (8S,20S,22R)-Des-A,B-22-methyl-cholestan-8,25-diol (Diol-3) in crystalline form. Diol-3 is the precursor of AGS-1 formed during the synthesis of AGS-1, and is characterized by the formula VII shown below:

Also disclosed herein is the compound (8S,20S,22S)-Des-A,B-22-methyl-cholestan-8,25-diol (Diol-4). Diol-4 is the precursor of AGS-2 formed during the synthesis of AGS-2, and is characterized by the formula VIII shown below:

Also disclosed are methods of purifying SAG-2, Diol-1, Diol-2 and Diol-3. The purification technique typically involves obtaining the SAG-2, Diol-1, Diol-2 and Diol-3 products in crystalline form by utilizing a crystallization procedure wherein the material to be purified is dissolved using as the solvent either ethyl acetate as the sole solvent to obtain Diol-1, Diol-2 and Diol-3 in crystalline form, or a mixture comprised of 2-propanol and hexane to obtain SAG-2 in crystalline form. In particular, it was determined that a mixture of about 10% to about 20% 2-propanol (v/v) and 90% to about 80% hexane (v/v) performed well. Preferably the mixture comprises about 15% 2-propanol (v/v) and about 85% hexane (v/v). Thereafter, the solvent can be removed by evaporation, with or without vacuum, or other means as is well known, or the resultant crystals may be filtered from the mother liquor. The technique can be used to purify a wide range of final products containing Diol-1, Diol-2, Diol-3 and SAG-2 obtained from any known synthesis, and in varying concentrations, ranging from microgram amounts to kilogram amounts. As is well known to those skilled in this art, the amount of solvent utilized may be modulated according to the amount of Diol-1, Diol-2, Diol-3 and SAG-2 to be purified.

EXAMPLES

The following examples are illustrative and should not be interpreted as limiting the claimed subject matter.

The usefulness and advantages of the present crystallization procedure is shown in the following specific Examples. After crystallization, the precipitated material was observed under a microscope to confirm its crystalline form. Yields of crystals were relatively high and the obtained crystals showed a relatively sharp melting point of 159° C. (SAG-2), 147-148° C. (Diol-1), 108-110° C. (Diol-2), and 133-134° C. (Diol-3).

The described crystallization process of the synthetic Diol-1, Diol-2, Diol-3 and SAG-2 products represents a valuable purification method, which can remove most side products derived from the synthetic path. Such impurity is the result of the contamination of starting raw materials. The crystallization process occurred easily and efficiently; and the precipitated crystals were sufficiently large to assure their recovery by filtration, or other means, and thus were suitable for x-ray analysis.

(20R,22R)-2-methylene-19-nor-22-methyl-1α,25-dihydroxyvitamin D3 (13.5 mg), was suspended in hexane (4 mL) and then 2-propanol was added dropwise to the suspension. The mixture was heated in a water bath to dissolve the vitamin, then was left at room temperature for about 1 hour, and finally was kept in a refrigerator for about 48 hours. The precipitated crystals were filtered off, washed with a small volume of a cold (0° C.) 2-propanol/hexane (3:1) mixture, and dried to give crystalline material. It should be noted that an excess of 2-propanol should be avoided to get the point of saturation, (i.e., only about 1 mole or less of 2-propanol should be added).

Experimental.

A colorless prism-shaped crystal of SAG-2 having dimensions 0.25×0.36×0.65 mm was selected for structural analysis. Intensity data were collected using a Bruker AXS Platinum 135 CCD detector controlled with the PROTEUM software suite (Bruker AXS Inc., Madison, Wis.). The x-ray source was CuK radiation (1.54178 Å) from a Rigaku RU200 x-ray generator equipped with Montel optics, operated at 50 kV and 90 mA. The x-ray data were processed with SAINT version 7.06A (Bruker AXS Inc.) and internally scaled with SADABS version 2005/1 (Bruker AXS Inc.). The sample was mounted on a glass fiber using vacuum grease and cooled to 100 K. The intensity data were measured as a series of phi and omega oscillation frames each of 1° for 10-15 sec/frame. The detector was operated in 512×512 mode and was positioned 4.5 cm from the sample. Cell parameters were determined from a non-linear least squares fit of 3541 peaks in the range of 4.0<theta<55°. The data were merged to form a set of 4787 independent data with R(int)=0.042.

The monoclinic space group C2 was determined by systematic absences and statistical tests and verified by subsequent refinement. The structure was solved by direct methods and refined by full-matrix least-squares methods on F2, (a) G. M. Sheldrick (1994), SHELXTL Version 5 Reference Manual, Bruker AXS Inc.; (b) International Tables for Crystallography, Vol. C, Kluwer: Boston (1995). Hydrogen atom positions were determined from difference peaks and ultimately refined by a riding model with idealized geometry. Non-hydrogen atoms were refined with anisotropic displacement parameters. In addition to one molecule of compound SAG-2, there was also one molecule of 2-propanol in the asymmetric unit. A total of 316 parameters were refined against 1 restraint and 4787 data to give wR2=0.1903 and S=1.246 for weights of w=1/[s2(F2)+(0.1150P2)], where P=[Fo2+2Fc2]/3. The final R(F) was 0.0768 for the 4787 observed data. The largest shift/s.u. was 0.001 in the final refinement cycle and the final difference map had maxima and minima of 0.579 and −0.456 e/Å3, respectively. The absolute structure was determined by refinement of the Flack parameter, H. D. Flack, Acta Cryst. A, vol. 39, 876-881 (1983).

The three dimensional structure of SAG-2 as defined by the following physical data and atomic positional parameters described and calculated herein (Tables 1-8) is illustrated in FIG. 1.

Crystallization from ethyl acetate. A mixture of Diol-1 and Diol-2 (0.17 g) in 2:1 ratio (based on 1HNMR) was dissolved in ethyl acetate (less than 0.2 mL) and left in the refrigerator to cool. The pure crystals (96 mg) of Diol-1, which had the highest concentration, precipitated first. The 22S absolute configuration of Diol-1 was established. The filtrate was concentrated and the obtained oil dissolved in ethyl acetate (less than 0.2 mL). The mixture was left in the refrigerator and pure crystals of Diol-2 (44.6 mg) were obtained. The 22R absolute configuration of Diol-2 was established. A second batch of pure crystals (16 mg) of the Diol-1 was obtained from the filtrate after second crystallization.

Experimental Analysis of Diol-1.

A colorless prism-shaped crystal of Diol-1 having dimensions 0.11×0.18×0.45 mm was selected for structural analysis. Intensity data were collected using a Bruker AXS Platinum 135 CCD detector controlled with the PROTEUM software suite (Bruker AXS Inc., Madison, Wis.). The x-ray source was CuK radiation (1.54178 Å) from a Rigaku RU200 x-ray generator equipped with Montel optics, operated at 50 kV and 90 mA. The x-ray data were processed with SAINT version 7.06A (Bruker AXS Inc.) and internally scaled with SADABS version 2005/1 (Bruker AXS Inc.). The sample was mounted on a glass fiber using vacuum grease and cooled to 100 K. The intensity data were measured as a series of phi and omega oscillation frames each of 1° for 5 sec/frame. The detector was operated in 512×512 mode and was positioned 4.5 cm from the sample. Cell parameters were determined from a non-linear least squares fit of 3987 peaks in the range of 4.0<theta<55°. The data were merged to form a set of 2821 independent data with R(int)=0.042.

The monoclinic space group C2 was determined by systematic absences and statistical tests and verified by subsequent refinement. The structure was solved by direct methods and refined by full-matrix least-squares methods on F2, (a) G. M. Sheldrick (1994), SHELXTL Version 5 Reference Manual, Bruker AXS Inc.; (b) International Tables for Crystallography, Vol. C, Kluwer: Boston (1995). Hydrogen atom positions were determined from difference peaks and ultimately refined by a riding model with idealized geometry. Non-hydrogen atoms were refined with anisotropic displacement parameters. A total of 190 parameters were refined against 1 restraint and 2821 data to give wR2=0.1078 and S=1.134 for weights of w=1/[s2(F2)+(0.0533P)2], where P=[Fo2+2Fc2]/3. The final R(F) was 0.0401 for the 2821 observed data. The largest shift/s.u. was 0.001 in the final refinement cycle and the final difference map had maxima and minima of 0.410 and −0.347 e/Å3, respectively. The absolute structure was determined by refinement of the Flack parameter, H. D. Flack, Acta Cryst. A, vol. 39, 876-881 (1983).

The three dimensional structure of Diol-1 as defined by the following physical data and atomic positional parameters described and calculated herein (Tables 9-16) is illustrated in FIG. 2.

Experimental Analysis of Diol-2. A colorless prism-shaped crystal of Diol-2 having dimensions 0.15×0.19×0.55 mm was selected for structural analysis. Intensity data were collected using a Bruker AXS Platinum 135 CCD detector controlled with the PROTEUM software suite (Bruker AXS Inc., Madison, Wis.). The x-ray source was CuK radiation (1.54178 Å) from a Rigaku RU200 x-ray generator equipped with Montel optics, operated at 50 kV and 90 mA. The x-ray data were processed with SAINT version 7.06A (Bruker AXS Inc.) and internally scaled with SADABS version 2005/1 (Bruker AXS Inc.). The sample was mounted on a glass fiber using vacuum grease and cooled to 100 K. The intensity data were measured as a series of phi and omega oscillation frames each of 1° for 5-10 sec/frame. The detector was operated in 512×512 mode and was positioned 4.5 cm from the sample. Cell parameters were determined from a non-linear least squares fit of 4485 peaks in the range of 4.0<theta<55°. The data were merged to form a set of 5680 independent data with R(int)=0.047.

The monoclinic space group P2(1) was determined by systematic absences and statistical tests and verified by subsequent refinement. The structure was solved by direct methods and refined by full-matrix least-squares methods on F2, (a) G. M. Sheldrick (1994), SHELXTL Version 5 Reference Manual, Bruker AXS Inc.; (b) International Tables for Crystallography, Vol. C, Kluwer: Boston (1995). Two molecules of Diol-2 were present in the asymmetric unit. Hydrogen atom positions were determined from difference peaks and ultimately refined by a riding model with idealized geometry. Non-hydrogen atoms were refined with anisotropic displacement parameters. A total of 379 parameters were refined against 1 restraint and 5680 data to give wR2=0.1103 and S=1.030 for weights of w=1/[s2(F2)+(0.0643P)2], where P=[Fo2+2Fc2]/3. The final R(F) was 0.0478 for the 5680 observed data. The largest shift/s.u. was 0.001 in the final refinement cycle and the final difference map had maxima and minima of 0.250 and −0.330 e/Å3, respectively. The absolute structure was determined by refinement of the Flack parameter, H. D. Flack, Acta Cryst. A, vol. 39, 876-881 (1983).

The three dimensional structure of Diol-2 as defined by the following physical data and atomic positional parameters described and calculated herein (Tables 17-24) is illustrated in FIG. 3.

A mixture of Diol-3 and Diol-4 (55 mg) in 2:1 ratio (based on HNMR) was dissolved in ethyl acetate (less than 0.2 mL) and left in the refrigerator to cool. The pure crystals (38.9 mg) of Diol-3, which had the highest concentration, precipitated first. The 22R absolute configuration of Diol-3 was established.

Experimental.

A colorless prism-shaped crystal of Diol-3 having dimensions 0.24×0.31×0.76 mm was selected for structural analysis. Intensity data were collected using a Bruker AXS Platinum 135 CCD detector controlled with the PROTEUM software suite (Bruker AXS Inc., Madison, Wis.). The x-ray source was CuK radiation (1.54178 Å) from a Rigaku RU200 x-ray generator equipped with Montel optics, operated at 50 kV and 90 mA. The x-ray data were processed with SAINT version 7.06A (Bruker AXS Inc.) and internally scaled with SADABS version 2005/1 (Bruker AXS Inc.). The sample was mounted on a glass fiber using vacuum grease and cooled to 100 K. The intensity data were measured as a series of phi and omega oscillation frames each of 1° for 5 sec/frame. The detector was operated in 512×512 mode and was positioned 4.5 cm from the sample. Cell parameters were determined from a non-linear least squares fit of 2476 peaks in the range of 4.0<theta<55°. The data were merged to form a set of 5350 independent data with R(int)=0.0689.

The monoclinic space group P2(1) was determined by systematic absences and statistical tests and verified by subsequent refinement. The structure was solved by direct methods and refined by full-matrix least-squares methods on F2, (a) G. M. Sheldrick (1994), SHELXTL Version 5 Reference Manual, Bruker AXS Inc.; (b) International Tables for Crystallography, Vol. C, Kluwer: Boston (1995). Hydrogen atom positions were determined from difference peaks and ultimately refined by a riding model with idealized geometry. Non-hydrogen atoms were refined with anisotropic displacement parameters. A total of 379 parameters were refined against 1 restraint and 5350 data to give wR2=0.1991 and S=1.047 for weights of w=1/[s2(F2)+(0.1134P)2], where P=[Fo2+2Fc2]/3. The final R(F) was 0.0872 for the 5350 observed data. The largest shift/s.u was 0.001 in the final refinement cycle and the final difference map had maxima and minima of 0.358 and −0.427 e/Å3, respectively. The absolute structure was determined by refinement of the Flack parameter, H. D. Flack, Acta Cryst. A, vol. 39, 876-881 (1983).

The three dimensional structure of Diol-3 as defined by the following physical data and atomic positional parameters described and calculated herein (Tables 25-32) is illustrated in FIG. 4.